In an known image forming apparatus, a pair of frames installed at the positions facing each other in the horizontal direction so as to sandwich an image forming unit therebetween are made of resin.
Meanwhile, a frame made of resin generally has less mechanical strength (bending rigidity) as compared with a frame made of metal. Therefore, a load due to its own weight of an image forming unit or the like is exerted particularly onto a portion on the lower side of the image forming unit. Accordingly, a distortion easily occurs to the lower side of a frame made of resin. When distortion occurs to the frame, stress acts upon the image forming unit and may cause a negative effect on image formation.